1. Field of the Invention
The present invention relates to wastewater treatment and more particularly relates to an improved method of sewage and wastewater treatment wherein sludge treatment or stabilization that produces a pathogen free sludge in short time by maintaining nitrous acid lends greater than 400 mg/L in a closed chamber so that the nitrous oxide will not be lost from volatilization from the reactor.
2. General Background
In the treatment of wastewater, a sludge product is generated. Proposed regulations (State and Federal) set criteria for reducing pathogens in the sludge process. This problem of pathogen reduction has been the subject of numerous articles. The following table (TABLE 1) lists references discussing processes to inactivate pathogens in wastewater sludges.
TABLE 1 ______________________________________ REFERENCES ______________________________________ 1. Blythe, R. D., 1989 "PSRP Research and Development Project for Synox Corporation," Report to USEPA Pathogen Equivalency Committee, Washington, D. C. 2. Reimers, R. S., Little, M. D., Culpepper, V. C., and Badeaux, R. D., 1990 "Results of the Effects of Sodium Nitrite on Ascaris Eggs Inactivation in Ozonics Processed Sludge," Unpublished Report. 3. Reimers, R. S., Little, M. D., Akers, T. G., Badeaux, R. D., and Metcalf, M. D., 1986 "Modification of Ozonics Sludge Treatment Process to Improve the Inactivation of Pathogens to meet PFRP Requirement", Tulane Report to Ozonics Corporation, Freehold, New Jersey, pp. 43. 4. Reimers, R. S., Little, M. D., Akers, T. G., and Henriques, W. D., 1990 "Evaluation of Ozonics Process to Inactivate Pathogens in Municipal Wastewater Sludges," Tulane Report to Ozonics Corporation, Gaithersburg, Maryland, pp. 51. 5. Subsey, M. D., Hall, R. M., Barrass, A. E., Blythe, R. D., Little, M. D., and Reimers, R. S., 19990 "Evaluation of the Synox Process for Disinfection of Raw Municipal Wastewater Sludge," WPCF Specialty Conference on the Status of Municipal Sludge Management for the 1990's, WPCF Publication, Alexandria, VA, pp. 3-27-3-40. ______________________________________
Recently issued U.S. Pat. No. 4,936,983, entitled "Sewage Sludge Treatment With Gas Injection," names Charles A. Long and Philip M. Grover as inventors. The '983 patent relates to an apparatus for treating sewage sludge in a hyperbaric vessel in which the sludge is oxygenated by injecting an oxygen-rich gas into the sewage sludge and then dispersing the mixture of sludge and oxygen-rich gas into the upper portion of a hyperbaric vessel for further interaction with an oxygen-rich atmosphere. The oxygen-rich gas is injected into the sewage sludge by delivering the gas to a combination gas and sludge mixing and dispersing assembly. The gas and sludge are mixed within a plurality of channels formed in the assembly before the mixture is dispersed from the channels. U.S. Pat. No. 4,936,983 is incorporated herein by reference.
The process of U.S. Pat. No. 4,936,983 is sometimes referred to as the "Synox" process such as, for example, in the above-listed WPCF publication.
The Synox process stabilizes municipal sludge by acidifying the sludge to a pH of between 2.5 and 3.5 in the presence of 200 to 300 ppm (parts per million) of oxygen at a pressure of 60 psi and a pure oxygen stream containing 3.0% to 6.0% ozone for a period of 30-90 minutes without additives, the process was ineffective against viruses and Ascaris eggs. These data indicate PSRP and PFRP inactivation criteria being met by the Synox process for bacteria only.